camera suddenly becomes unresponsive and stops working
Potential causes and solutions
camera is accidentally recording a video
in this situation, you should be seeing an active live view image and REC should be displayed
stop the video recording by pressing the REC button or perhaps the shutter button on some cameras
camera is taking a long exposure
this may have occurred if the lens cap is on, or it is very dark such as with night astrophotography
note that most cameras by default will also take a second long exposure after the first - this is called a dark frame image and is used by the camera to reduce long exposure sensor heat-induced noise from the first image
some cameras such as the Olympus OM-D E-M1 mark II displays a live update of how much longer the second image exposure will take
DO NOT turn the camera off unless you are happy to lose the image and potentially corrupt the memory card
buffer is full
this usually occurs after you have shot a burst of images, and the camera is still saving them to the memory card
the camera should display a waiting icon
DO NOT turn the camera off unless you are happy to lose all these images and potentially corrupt the memory card
INSTEAD, WAIT until the buffer empties
battery is flat
replace battery with a fresh battery
camera's algorithms hit a brick wall
this occasionally can happen, especially with new firmware upgrades which have not been fully tested by the manufacturer
try turning the camera OFF then back ON
if that doesn't work, take the battery out then replace it, and turn it on
if that fails, you may need to take it in for repair
camera is dead
this may occur due to water damage, dropping the camera, wear and tear, etc